The present invention relates, most generally, to semiconductor devices and methods for forming the same. More particularly, the present invention relates to trench capacitors formed on silicon-on-insulator substrates.
Semiconductor devices typically utilize a multiplicity of capacitors to perform various charge storage functions. Capacitors include two electrodes isolated from each other by an insulating material referred to as a dielectric. Electrodes are commonly formed of conductive or semiconductive materials. According to conventional semiconductor manufacturing methods, capacitors are xe2x80x9cvertically stackedxe2x80x9d and include a horizontally formed dielectric material which insulates conductive or semiconductive materials formed above and below the is dielectric. Materials used as conductive materials include various metals, and materials used as semiconductive materials include doped polysilicon and other films, as well as the silicon substrate itself. The ability of a capacitor to store charge depends on the capacitor area. Since conventional stacked capacitors are formed above the surface of the semiconductor substrate, as the area of the capacitor increases to enhance the charge storage ability of the capacitor, it does so at the expense of substrate surface area which might otherwise be used for other device features. As a result and in order to minimize the surface area occupied by capacitors, trench capacitors have become highly favored in the semiconductor manufacturing industry.
Trench capacitors extend down from the surface of the semiconductor substrate and include a capacitor area which increases as does the depth and width of the trench opening in which the trench capacitor is formed. It can be therefore understood that the charge-storage ability of the capacitor can be increased by simply increasing the depth of the trench and not at the expense of substrate surface area. Trench capacitors are therefore highly favored.
Recent trends in the semiconductor manufacturing industry have been towards the use of silicon-on-insulator (SOI) substrates. SOI substrates are favored because active devices formed within the upper silicon layer, are insulated from the bulk substrate. Therefore, device leakage through the substrate is minimized and other problems associated with being electrically coupled to the substrate, are avoided. The use of SOI technology, however, presents a problem since the trench openings commonly used to form trench capacitors, must extend through the insulating layer of the silicon-on-insulator substrate in order for the trench capacitor to have a sufficient capacitor area. The problem results because the outer of the trench capacitor electrodes is the substrate region which bounds the trench opening. The trench opening is filled with a dielectric liner which insulates the other electrode, commonly a plug formed of a semiconductor material disposed within the trench, from the outer electrode. A shortcoming associated with the use of trench capacitors in SOI technology is that the outer capacitor electrode is insulated from the substrate surface by the insulator film of the silicon-on-insulator substrate structure and cannot be easily contacted. An alternative approach for integrating capacitors into SOI technology would be to revert to stacked capacitors formed above the substrate surface and which include a capacitor area which comes at the expense of device geometry. In these days of advancing device integration, this particular approach is not favored.
The present invention addresses these issues and provides a space saving trench capacitor which is compatible with SOI technology.
The present invention provides a method for forming a semiconductor device including a trench capacitor compatible with SOI technology. The trench capacitor extends through the upper silicon layer and the insulating layer, and extends into the semiconductor base substrate beneath the insulating layer. The trench capacitor includes an inner electrode formed within the trench opening and surrounded by a capacitor dielectric material. The trench capacitor also includes an outer electrode which is electrically coupled to a contact structure formed in close proximity to the trench capacitor. The outer electrode may include portions of the base semiconductor substrate which bound the trench opening, portions of the silicon layer which bound the trench opening, or both.
The method includes forming an associated contact structure in close proximity to the trench capacitor by providing a silicon-on-insulator substrate including a silicon layer formed over an insulating layer formed over a base substrate, forming a duality of trench openings that extend into the base substrate, thermally oxidizing to selectively form an oxide liner on one of the trench openings, and filling each trench opening with a semiconductor material. The contact structure includes a semiconductor material formed in a trench which extends through the insulator material and is thereby electrically coupled to the outer trench electrode which includes portions of the base semiconductor substrate which bound the trench capacitor.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but not restrictive of the invention.